One major problem with client/server applications for manipulating images lies in their lack of reactivity. This is because the time elapsed between the request for an image by a user and the display of the image requested on the client machine of the user often proves to be unacceptable from the point of view of the users.
A first solution to the problem indicated above can be found in the progressive display of the image requested. In this case, the application does not await the entire reception of the data in order to start the display of the image requested. A first degraded version of the image is first of all displayed, and then this is refined as the data are received.
An image format allowing progressive display is however necessary for implementing such a solution. This is because an image must be capable of display even when the bitstream of the image has been received only partially. In addition, if the bitstream is capable of partial transmission, the question of the order of transmission of the data is then posed and need to be resolved.
A second solution to the problem indicated above consists of preserving the data in the cache memory of the client device. In this way, a multiple transmission of identical data is avoided. This approach makes it possible to reduce the display times of the data when the latter are already present in the cache memory.
Concerning the progressive display and the organization of the transmission of the data in the bitstream, software referred to as Kakadu (registered trade mark) is known in the state of the art, developed by David Taubman in the context of the JPEG2000/JPIP standard.
In the Kakadu software, the elementary entities of the bit stream, referred to as “precincts” and corresponding to spatial positions of the image, are ordered so as to first of all send the precincts situated at the center of the image. Such an approach has the drawback of taking as its assumption the fact that the interesting parts of the images are at the center of them. This assumption is ill-founded since the interesting areas may just as well be situated on the peripheral parts of the images.
Concerning the preservation of data in the cache memory of a client device, various solutions have been proposed and form part of the state of the art.
Thus protocols are known in which “cache” and “no cache” commands are provided for indicating explicitly to proxy servers, the data which must or must not be placed in cache memory. The following protocols, in particular, are known to the inventors for supplying cache management commands:                the protocol RFC2616—Hypertext Transfer Protocol—http/1.1.;        the protocol RFC1945—Hypertext Transfer Protocol—http/1.0.; and        the JPIP protocol presented in JPEG2000 Image Coding System—Part 9: Interactivity Tools, APIs and Protocols—Final Committee Draft. ISO/IEC JTC1/SC29 WG1 N3052, R. Prandolini, S. Houchin, G. Colyer, 25 Jul. 2003.        
The approaches adopted in the above protocols have in particular the drawback of not allowing suitable management when the space available or released in the cache memory is not sufficient to store the data recently received. In addition, in these protocols, the server device explicitly manages the cache memory of the proxy. Such a technique is difficult to manage when the server device is in communication with many client devices.
In the article Caching schema for mobile web information retrieval, 2nd International Workshop on Web Dynamics, in the 11th International World Wide Web Conference, May 2002, a method is described, in the field of Internet applications, for managing cache memories according to which data (web pages, metadata, etc) are prestored in the cache memory of a portable multimedia unit (portable electronic organizer, portable computer, etc). However, in this method, the selection of the data to be stored must be done manually by the user. Once stored, the data can be deleted from the cache memory or be updated according to the geographical position of the portable multimedia unit.
The need for intervention by the user in the above method is a drawback and it would be desirable for all the tasks relating to the management of the cache memory to be carried out automatically or almost automatically.
Still in the field of the Internet, there are also known, through U.S. Pat. No. 6,574,715 (IBM) a method and device for managing internal and external caches in a data processing system. In accordance with this method of IBM, a server stores modifiable web pages either in a local cache or in external caches situated for example in proxy agents. The selection of a cache, local or external, is carried out according to a degree of change in the web pages. A process of verifying consistency between the pages stored in the external caches and those stored in the local cache is implemented by the server.
In this IBM method, the management of the external caches of the proxy agents is centralized by the server. Consequently the application of the external cache management functionalities of this method to the management of caches of several client devices in a client/server application does not enable a client device to manage its cache itself.